The present invention relates to a mill for comminuting a food product.
Devices for comminuting a product, such as a food product, are well known in the art and typically comprise a rotating impeller having a plurality of generally radially extending blades disposed within a generally annular array of fixed, circumferentially spaced apart knives. During the past 25 years, these devices have been manufactured with an inside diameter of the annular knife array of approximately 6 inches. Although the impellers of these known devices may be operated at speeds up to 12,000 revolutions per minute, they are typically restricted to approximately 10,300 revolutions per minute to prolong the impeller bearing life. These devices have proven superior in their size reduction ability to any other commercially available equipment. Examples of such devices can be found in the following U.S. Pat. Nos. 3,251,389; 3,51,557; 3,608,598; and 3,888,426.
Recently, homogenizers have been introduced into the commercial arena that are capable, under some circumstances, of producing a comminuted product similar to that produced by the aforementioned mills. The homogenizers, which have found particular acceptance in the field of manufacturing peanut butter and ketchup, typically comprise a reciprocating piston moveable in an open ended cylinder. The open end of the cylinder is closed by a ball or plate that is tightly pressed against the end of the cylinder by a heavy spring. Movement of the piston away from the open end draws the product into the cylinder. Then, as the piston is advanced toward the open end, the pressure exerted on the product forces the ball or plate slightly away from the open end such that a thin stream of product is squirted out of the cylinder at a very high speed against a stationary surface. The destructive forces acting on the product rupture it into small particles. The homogenizers, while generally successful, require extensive, and therefore costly, maintenance and pose some danger to the operating personnel due to the high internal pressures applied to the homogenizer structure. Also, the product must first be reduced to a liquid before it can be pumped into the homogenizer.
In all of today's methods of making peanut butter, the roasted and de-skinned peanut halves are first converted into a hot liquid by passing them through a Bauer-type mill. The Bauer-type mill consists of two circular plates with the flat surfaces slightly separated and facing each other. These facing surfaces have bumps or protrusions that grind the peanuts when they are fed to the centers of the plates with one of the plates rotating at a high speed.
One of the present methods of making a high quality peanut butter is to pass the product from the Bauer-type mill through a series of rotating mills of the afore-described type. Passing the product through this plurality of rotating mills (typically two such mills are utilized) further reduces the sizes of the peanut particles. A swept wall heat exchanger is used between the two rotating mills to cool the peanut butter before it enters the second mill. It is also known to substitute the use of a homogenizer for the plurality of rotating mills to produce the final peanut butter product.
Tomato ketchup is made from ripe tomatoes after removing the skin, the seeds, and a portion of the water. Vinegar, sugar and spices are added to produce the flavor. The amount of insoluble material and its characteristics vary considerably with different batches of tomatoes. All ketchup manufacturers use some method to reduce the particle size of the insoluble material in the ketchup. Generally speaking, the smaller the particle size, the thicker will be the ketchup. The small particle size presents more surface area to collect the liquid, thereby increasing the viscosity of the product. At the present time, some manufacturers use rotating mills to produce their product, others use only homogenizers, while still others utilize a combination of the two devices.
The Bostwick test is a standardized test to determine the viscosity of a ketchup product. The test is made with a channel which is 5 cm wide by 3.8 cm in depth with the ends of the channel closed. A moveable gate is located across the channel at a distance of 5.2 cm from one end. The ketchup is poured into the box so as to be level with its top and the gate is raised to permit the ketchup to run lengthwise beyond the gate opening. The bottom of the channel is marked in centimeters and, after 30 seconds, the viscosity is determined by measuring the distance in centimeters the ketchup has moved into the channel. This distance represents the Bostwick number for any particular test.